Improving the knight's position.
13. c2c3  13... d7d5 So far, everything is very familiar in the theory of the Berlin Defense. White's system is very solid and illustrates one of the problems of Black's opening choice for non-elite players: White plays for two possible outcomes, a perspective that (rightly) doesn't make amateur players very happy with Black's position. 14. b1d2  14... c8f5 Supposedly White plays the bishop to d3 to prevent this move, so putting the bishop on f5 has to be critical against 14.Nd2. 15. e1e3 